Method of treating iron ores containing chromium



March 5, 1957 KIYOTO MATSUZUKA 2,784,074

METHOD OF TREATING IRON ORES CONTAINING CHROMIUM Filed Nov. 5, 1953 3Sheets-Sheet l Lateriie Edge runne ----Soda ash 8: .Lime

Pug mill Roastin {urnace Leaching tank Leached Solution Pel letPrecipitation & Separation of Aluminium Hydroxide Precipitation 5:Separation 0\ Sodium Dichromate JNVEN TOR.

Ki/a To MHTSl/l u A March 5, 1957 KIYOTO MATSUZUKA METHOD OF TREATINGIRON ORES CONTAINING CHROMIUM Filed NOV. 5, 1953 3 Sheets-Sheet 3 ON 9 0+1 N O m 0 3 w ows zifiQwoqm Q2 w RON 5 mvq ou z KI BY United Statesatento METHOD OF TREATING IRON ORES CONTAINING CHROMIUNI Kiyoto.Matsuzuka, Kumamoto-ken, Japan, 'assignor to Yawata'lron & Steel Co.,Ltd.,'Tokyo, Japan Application November 5, 1953,, SerialNo. 390,,376Claims-priority, application Japan February 14, 1953 9 Claims. ,(Cl.75-3) This invention relates to a method of removingchromium from ironores containing chromiumand particularly to a method of recoveringchromium from l-ateritic ore and of making .said ores especiallysuitable as raw materials for producing iron.

Laterite is representative of iron ores containing chro' mium and it isas such representative thatit .is dealt with in the following. lateriteas .known is an -air-slaked product of serpentine and the amount of itsdeposits is said to be inexhaustible. It .is produced in quantitiesinevery country of the world. Laterite, .for example, produced in thePhilippines contains 47.7 to 51.4% Fe, 2.10 .to 2.74% Cr, 4.50 to 7.52%A1203, 1.90 to 3.33% SiOzand small amounts of Ni, Co and Mn. The mainconstituent of this ore is ferric oxide. The result :of analysis by heatshows that this ore has 5.5% water of crystallization at 200 to 250 C.It can be presumed from theamount of dehydration that all F6203 existsin ,the .form of FezOs-HzO (needle iron ore). Needless tosa-y, zit isjudged from the constitution of said me that some gelled iron oxidecontaining water and F62O3'3Ha0 also exist. Alumina seems to exist asAlz'Oa'3H2O or rAlzOs-H2O. Silicic acid exists as silica, gelled silicic.acid andsilicate. Chromium exists mostly as chromite .(FeO-CrzOs) andpartly as chromate. The chromiteis so 'britt'le in nature that it'can beeasilycrushed by finger tips. Its grains are so fine as to he muddy. Thefine grains of-limonite-are adsorbed by chromite or envelop chromite;this state continues the same all through to thefinegrains of chromite.When both of these minerals are crushed for physical separation,chromite will be readily finely .ground, will become colloidal and willbe very difficult to.separate by gravity or any other method. This isthe maincause of the difiiculty of dressing this ore. Asregardsithematter of removing chromium for the sake of utilizing .laterite,various methods have been tested and reported in the United States onores produced in Cuba, and in Japan on ores -produced in the Philippinesand Japan proper. These respective methods and the results of laboratorytests are discussed in the following.

(1') DRESSING BY GRAVITY This is to utilize the diiference of specificgravity between iron ore and chromite. In "U. S. Patent No. 2,363,315aiming at separating nickel and chromium from Cuban laterite, Mr. John.D. Grothe purports to achieve separation by utilizing vthe difierencenf'specific gravity between magnetite 1(551 specific :garvity) producedby reduction and roasting and chromite 01:4 specific gravity); in thecase iof.removing-chromium'this method being especially .namedflotation. .However, it:1is :found in the light of the theory indressing Jthat'rsu'ch ".fine fgrains cannot :be .well separated -by the.-':specific gravity difference of 0.7. .As the .assignee of patentee,;Dnrr Company, confesses, this method dustrialized.

2 ,2 DISPERSION When :laterite is lthrownintowater and stirred, itwillreadily collapse and will sink down :after .:a while. Howeve1:,;if 2a:small amount of *a dispersing agent :such as :for example, alkali isadded thereto and the mixture:is:stirred and :left alone, the finegrains of ilimonite will .be "dispersed and floated. The depositcontains comparatively much chromium. Itris intended to attain the.o'bject 'of :dressing by separating the .floating substance and the\deposit by an adequate method. The results of testsma'de by using NaOHas .a -dispersing agent on an Omonhon specimen (containing 2.74%chromium) are now listed in the following:

-. Raw Dispcrsing Dispersed Substance No. .Material Water Agent,20%Weight Chromium in g. in l. 'NaOH in inPercent inPercent :300 6; -20i 4bLL33 As seen'from the above results of experiments, in'this method, .thepercentage of the removal of chromium is low (below 50%) and thepercentage of collection of can diardly he reliably :iu- I iron ores isbelow 50%, being out of the question.

This method was named emulsion dressing by the Heavy Metal ResearchLaboratory established in Japan during "World War II. n is found in thelight of the reports of experiments made by this method on various kindsof laterite produced in various producing places as published 'inReports of the Heavy Metal Research Ins'titue, 1st edition, December1944, that, though some favorable results have been shown in someproducing places, the percentage of the removal of chromium and thepercentage of collection of iron ores are not favorable and thedrying-operation after separation is difiicult. 'In view of suchresults, this method is-never'suited to treatment of large quantities.

(3) ADDITION OF SODA ASH fE-his AIS like the method of the presentinvention to be described later and is a method wherein chromium isextracted as sodiumchromate by merely adding soda ash to therawm'aterial and heating the mixture as in manntfacturing usual sodium.c'nromate without any combination with pelletizing. Mr. McCormackapplied this :method :to :Cuban iores as easly :as 1926 but "the resultshowed-that the extraction of chromium was quite insutfi- .cient .-(-E.-Erary: The Aluminum industry, p. 142). .I, the present inventor, havefirst experimented Omonhon ores byrthis method. The percentages ofextraction' were 57.7,, 5.9.0, .-63. 6-and 87.2% against the amounts ofaddi- :tion ,of .soda ash :of 5, 10, 20 and 30%, respectively,- at .theheating temperature of 700 C. for 30 minutes. .These .resultsare notfavorable as compared with those of the method .of this invention,partly due to the low temperature. .After extraction, reheating :at ahigh tern;

perature .is necessary to obtain powdered ziron ores and This method-iscovered by S. Patent No. 2,584,700 "011 a :method not treating iron orescontaining nickel and chromium invented by Mr. C. R. Hayward. Thispatent .is owned hy FBethlehem Steel Company. This -=method isalsoitoztreat Mayaricores producedfinictiba assumrnarized rin'tthetfollowing'. al'iirst of tall, I laterite' 'is trea'ted stilphuric acid.Insoluble chromite and silicic acid are removed. Parts of iron, nickel,aluminum and chromium are then replaced by iron powder thrown in and areprecipitated. The remaining iron solution is evaporated, dried andsolidified as iron oxide. Sulphur dioxide produced then is utilized forsolution. However, the operation in this method is complicated andcannot help being uneconomical, being not a method suited to treatmentof large quantities.

An object of this invention is to provide an improved industrial methodof extracting chromium from iron ores containing chromium andparticularly from laterite.

Another object of this invention is to provide a method of making ironores containing chromium and particularly laterite raw materialssuitable for producing iron.

Further objects of this invention will become clear from the followingdescription. 1

According to the method of this invention, soda as and/or lime are/isadded to laterite and the mixture is ground and mixed. The mixture ismolded into pellets and is roasted in an oxidizing atmosphere in afurnace to convert chromium contained in the laterite ore into sodiumchromate. Then, by immersing the roasted products in water or a solvent,the sodium chromate content is dissolved out and the solid part isseparated. Chromium is recovered from the solution. The remaining solidpart has very low chromium content and is very suitable as a rawmaterial for producing iron.

Figure 1 of the drawings is a flow sheet showing a mode of working themethod of this invention.

Figure 2 shows the precentages of extraction of Cr, Na, Al and SiOz when15% NazCOa and various percentages of Ca(OH)2 were added to laterite andthe mixture was treated by the method of this invention.

Figure 3 shows the constitution of pellets obtained by adding 15% NazCOsand various percentages of Ca(OH)z to laterite as in the case of Figure2 and by treating the mixture by the method of this invention.

Figure 4 shows the percentages of extraction of Cr and Al when variousamounts of Ca(OI-I)z were added to 12.5, 15, 20 and 25% NazCOs and themixtures were treated by the method of this invention.

Figure 5 shows the weight in percentage of Cr remaining in the pelletobtained by treatment under the same condition as in Figure 4.

In the present invention, laterite alone or with the addition of anadequate amount of iron ores or any other raw material for producingiron is first finely ground by means of a grinder. The grinder to beused may be an edge mill or any other known grinder. The size of aground grain is preferably such as will pass through a 200 mesh screen.

Soda ash or a mixture of soda ash and quick lime in a powdered state inan amount adequate depending on the chromium content is added to theground iron ores containing chromium and is intimately mixed together.Slaked lime may be used in place of the above quick lime. In mixingthem, an adequate amount of water is added for convenience inpelletizing. This water may be fed by adding said soda ash or mixture ofsoda ash and lime as a solution or suspension. This mixture is thenmolded into pellets of an adequate size and shape which are preferablyof a column 20 to 30 millimeters in diameter and to millimeters long. Ifthe pellet is made a holed pellet by making one or severalthrough-extending holes in the central part thereof, the below mentionedpercentage of extraction will be improved, because, in the belowmentioned roasting, oxygen will come into contact with the interior ofthe pellet and, in extracting, the entry of water into the interior willbe madeeasier. When the molded mixture is enclosed in a furnace such asa roasting furnace and is heated at a temperature of 900 to 1200" C. orpreferably 1000 to 1100 C. in an oxidizing atmosphere, roasted-pelletscan be. produced. By this heating, the

chromium content in the pellets will be converted to sodium chromate bythe following reaction:

In case sodium carbonate NazCOs only is used, sodium chromate will beobtained by the following formula:

The sodium chromate thus obtained is very easily soluble in hot water.Therefore, if the roasted pellets while at a high temperature are throwninto and immersed in water which is preferably warm, the greater part ofthe sodium chromate will be extracted as dissolved. It is preferable tostir the solution in the above immersion. In the above roasting of thepellets the roasted pellets become porous due to the volatilization, ofwater of crystallization of limonite. Therefore, in extracting sodiumchromate, water can readily penetrate into the interior of the pelletand sodium chromate can be further dissolved out. Such solvent as, forexample, sodium sulphateor calcium carbonate solution may be usedinstead of the above water. The effects of adding the above soda are asfollows:

(1) The iron content is at first limonite but, when heated, becomeshematite. The surface temporarily becomes ferrite due to soda butdecomposes and again becomes hematite. A part remains as ferrite but,when made to act with water, becomes hematite and caustic soda. Thiscaustic soda helps the growth of sodium chromate.

(2) Alumina existing as bauxite loses water of crystallization andcombines with soda at 550 to 600 C. and leaches out as sodium aluminate,improving the quality of the iron content. The production of alumina asa byproduct from ores containing a large amount of alumina and a smallamount of silicic acid can be considered.

(3) Silicic acid existing as silica or silica gel combines with soda,becomes sodium silicate and is leached out by water, also serving toimprove the quality of the iron content.

The effects of adding lime are as follows:

(1) Lime with the addition of either CaO or Ca(OH)2 combines with CO2obtained by the production of sodium chromate, sodium aluminate orsodium silicate and becomes CaCOs, serving to increase the strength ofthe pellets.

(2) Soda is prevented from acting with alumina or silica and the loss ofsoda ash is prevented. (In the case of producing alumina as a by-productor of requiring high quality pellets as mentioned above, the amount tobe used is limited.)

If the chromium content of the extract obtained by the treatment asmentioned above is concentrated after impurities are removed and is thentreated with concentrated sulphuric acid, sodium chromate will becomesodium dichromate. It can likewise be made potassium dichromate orchromate by a known method. On the other hand, the pellets from whichchromium content has been removed can be used as they are as rawmaterials for producing iron.

Examples of this invention are shown in the following to help it to beunderstood. However, this invention is not to be limited to theseexamples.

Example 1 PELLETIZING OF IRON ORES CONTAINING CHROMIUM AND ALUMINUM (ANEXPERIMENT BY THE EXTRU- SIVE METHOD) The specimen used in theexperiment was Philippine Omonhon laterite and its chemical compositionwas 50.1% Fe, 2.1% Cr, 7.5% A1203, 1.9% SiOz, 10.6% combined water andsmall amounts of Ni, CO, Mn, etc.

This specimen was first ground to grains finer than 200 mesh by meansofan edge runner as shown in Fig. I. Soda ash (sodium carbonate) andslaked lime in a state of solation or suspension were added to the abovespecimen and the mixture was well mixed by means of :a mixer. Then themixture was extruded into the shape-of a column .by means of an Augertype pug mill and 'was cut into pellets each 20 millimeters in dimeterand millimeters long.

These pellets were put into a roasting furnace, were heated for an hourat 1 100" C. to 1200 C. in an oxidizingatmosp'here, were -then'thrownwhile still at a high temperature (about 500 G.) into an extracting tankprovided with :an agitator and were subjected to extractionfor l to 2hours with the water temperature kept at'70 to 80" C. The greater partsof chromium and aluminum "were extracted during .the first hour and al-Example 3 Pellets were .made in the same way as .in Example 1. exceptthat they were cylindricalpelle'ts each '20 millimeters in diameter and20 millimeters 'long with a 'hole 5 millimeters india'meter made throughthe ceriter 'the're-.

. y g u of. The "amounts of addition in percent of Na2COs most .Dflhemwere extracted i t two Hours and Ca('OH')2 and the 'perce'ntagesof"extraction of Cr 5222a? Hated and was treated with Concentratedsulphuric acid pellet without a hole being also shown for information.to ."produce sodium 'c'lichromate. Ihetpercentages of the aboveextraction were as shown .in Fig. 2. As more than 1', Percentages'offExtraetion 15% Na evaporated in roasting, it could be separatelyNaooa recovered and utilized. .As .seen .in'the figure, the .pergcentageof extraction of Cr and Al was .the best at 2 I rigggg am:

to 4% of added Ca(OH)2. The percentage of extractinn *of ;SiO z;.waslower. The percentages by weight of Percent Percent Pmem I .Pmem

the compositions of the pellet produced by the above- 10 12 72 2 .00mentioned method were .as shown in Fig. 3. They decreased a little withthe increase of Ca(OH)2 at 60% iron content. With the addition of 3%Ca(OH)2, Fe

was 59.0%,Na20 was lQ.4:-%,.Al203 was 2.1% and S102 As in the above. theipercentege extraction of was 2.0%. The'compressive strength of thispellet was Chr mium Cmlld be increased by 6 to 12% by making 10 kg. andits specific gravity was 3.45. a hole in ithepellet. Almost the sameresults were ob- Theipercentages of extraction in case the amount ofmined in sp aluminum CaIOH): was van'ed against *the'amounts of 12.5,15, 20 Example 4 and '25% NazCOs are shown in Fig. -4. As seen from saidfigure, Cr-showed the maximum'value of 85% at Pellets for Producing Ironcould-be made Y Yemctvmg 17.55% Naz'COs and more than 90% at both 15 andCr and by Ihe Same e hod as in the abovefrom a 20% N co A '1 5%, h i 1 fC O product from which Ni and Co have been removed by was 2 to 4% but,at 20%, it was 6 to 8%. The perthe wet or dry Process. Ni-and 9 were e ey the centage of extractiqn at 25% NazCOs was lower than 40 Wet Q f Q QP 111 the I pp and at 20%. It was found that the increase of the amountcfiiltamlng 54-08% Fe, 03% 232% of extraction of Al in proportion to theamount of ad- 192% A1203 and 2 5102- sodajmd 4%11me dition of Na2CO3 wasmore remarkable than that of Cr. M H) were added to the abeve reslduesand the Fi 5 shows th h i contents of h ll mixture was heated for anhour at 1100 C. and was subdu d against th a t f dditi of jected toextraction for two hours. Thus the percentage NMCOaCMOHh of extractionof Cr of 85% was obtained. shown in Fig. 3. The minima of Cr against12.5, 15, Examples 540 20 and 25% NasCOs were 0.42, 0.24, 0.19 and0.18%, Laterite ores containing d chromium. respectively. Especially,with the increase of Naacos, respectively, were ground t grains finerthan 200 m hthe strength of the pellet decreased. The compressive Powdre soda ash nd q lck lime were added to said strength of 10 kg. of thepellet at 15% NazCOs and 3% ground laterite and the mixture was wellmixed to be a Ca(OH)s lowered to that of 7 and 3 kg., respectively rawmaterial for pelletizing by a balling mill. The condiat the samepercentage of Ca(OH)2 but at 20 and 25% tions and results were as listedbelow.

Chromium Chromium Amounts of Percentage Examples content in AdditivesTempera- Time (hours) Remaining Extraction 0i Extraction the ore inPercent; tures, O. inPellets in of Chromium oi Chromium Percent inPercent 205 13 soda ash. 1.000 0.5 0. 40 1.66 80.0 2.05 -do 1.000 1.00.28 1.77 20.0 2.05 do 1.000 2.0 0.23 1.83 89.2 2. 2 10 soda ash, 1. 0000. 5 0. 36 1. s4 s2. 7

71irne. 2.2 do 1.000 1.0 0.20 1.04 88.2 2.2 do 1.000 2.0 0.18 2.03 02.3

NazCOa. Therefore, the decrease of strength could be In case the heatingtemperature was 1100 to 1200 C., compensated by increasing the amount ofaddition of the heating time could be further reduced and yet theCa(OH)z. Generally, the most favorable amount of same results could beobtained. addition of Ca(OH)2 is A to /3 the amount of addition Thepellets from which chromium was thus removed of NaCOa. However, theabsolute values of the amounts contained 57% iron, were good in bothstrength and reof addition of NazCOa and C8.(OH)2 vary depending onduction rate and could be made raw materials for prothe composition ofthe raw material to be used or parducing iron as they were. ticularly onthe contents of Cr and Al to be extracted Now the features of the methodof this invention are and on whether Cr only is to be removed as alay-product 75 enumerated as follows:

or both Cr and A1 are to be removed.

(1) If water is added to laterite in the wet treatment,

it will take a long time for precipitation and drying, such method beingunecouomical. The method of this invention wherein the dry treatment isutilized is advantageous.

(2) In this method, the characteristics of laterite are ingeniouslyutilized and the property which would be very troublesome in theordinary method proves all the more advantageous.

For example, (i) chromite which is brittle in nature and is apt to bepowdered is all the more favorable in completely acting with soda ash.(ii) It is almost impossible to ideally separate limonite adsorbedaround chromite. However, in this method wherein the material is finelyground from the first,,the above disadvantage has no effect whatsoever.(iii) Iron oxide and alumina have water of crystallization (8.5% at 200to 250 C.). When the pellet is heated, said water of crystallizationwill volatilize and the pellet will become porous. This will facilitatethe circulation of air, promote the growth of sodium chromate and alsofacilitate leaching with water, increasing the percentage of removal ofchromium.

While this invention has been described in the above chiefiy'withrespect to laterite, it will be easily understood that the same can beapplied to any other iron ores containing chromium.

What I claim is:

i. A method of producing pellets containing substantially no chromium,said pellets being suitable as raw material for the production of iron,which method comprises grinding an iron-bearing material comprisingchromium and aluminum, adding to the ground material (a) a suflicientquantity of soda ash to convert at least the chromium into a sodium saltthereof and (b) lime in an amount of at least about A the quantity ofadded soda ash, intimately admixing said materials, adding to theresultant mixture sufiicient water to enable the mixture to be molded,molding the aqueous mixture into pellet form, heating the thus-obtainedpellets to 900- 1200 C. in an oxidizing atmosphere, extracting thethustreated pellets with an aqueous liquid, whereby at leastsubstantially all the chromium is extracted therefrom.

2. A method according to claim 1, and recovering sodium salt of chromiumfrom the aqueous extract.

3. A method of producing pellets containing sub: stantially no chromium,said pellets being suitable asraw material for the production of iron,which method comprises grinding an iron-bearing material comprisingchromium and aluminum, adding to the ground material (a) a sufiicientquantity of soda ash to convert at least the chromium and aluminum intosodium salts thereof and (b) lime in an amount of at least about $4 thequan: tity of added soda ash, intimately admixing said materials, addingto the resultant mixture suificient water to enable the mixture to bemolded, molding the aqueous mixture into pellet form, heating thethus-obtained pellets to 900-1200 C. in an oxidizing atmosphere,extracting the. thus-treated pellets with an aqueous liquid, whereby atleast substantially all the chromium and aluminum are extractedtherefrom.

4. A method according to claim 1, wherein the heating or the pellets iscarried out at 1000 to 1100 C.

5. A method according to claim 1, wherein the iron. bearing material islaterite ore.

6. A method according to claim 1, wherein the pellets are extruded intohollow pellet form.

7. A method according to claim 1, wherein the aqueous liquid is warmwater. 8. A method according to claim I, wherein the moldinginto pelletform is effected by extrusion. I 9. A method according to claim 1,wherein the molding into pellet form is eifected in a balling mill.

References Cited in the are of this patent UNITED STATES PATENTS GreatBritain May 5, 1927

1. A METHOD OF PRODUCING PELLETS CONTAINING SUBSTANTIALLY NO CHROMIUM,SAID PELLETS BEING SUITABLE AS RAW MATERIAL FOR THE PRODUCTION OF IRON,WHICH METHOD COMPRISES GRINDING AN IRON-BEARING MATERIAL COMPRISINGCHROMIUM AND ALUMINUM, ADDING TO THE GROUND MATERIAL (A) A SUFFICIENTQUANTITY OF SODA ASH TO CONVERT AT LEAST THE CHROMIUM INTO A SODIUM SALTTHEREOF AND (B) LIME IN AN AMOUNT OF AT LEAST ABOUT 1/4 THE QUANTITY OFADDED SODA ASH, INTIMATELY ADMIXING SAID MATERIALS, ADDING TO THERESULTANT MIXTURE SUFFICIENT WATER TO ENABLE THE MIXTURE TO BE MOLDED,MOLDING THE AQUEOUS MIXTURE INTO PELLET FORM, HEATING THE THUS-OBTAINEDPELLETS TO 9001200*C. IN AN OXIDIZING ATMOSPHERE, EXTRACTING THETHUSTREATED PELLETS WITH AN AQUEOUS LIQUID, WHEREBY AT LEASTSUBSTANTIALLY ALL THE CHROMIUM IS EXTRACTED THEREFROM.